Morphology of pre-noon and post-noon auroras

Abstract

General characteristics of dayside auroras for quiet and disturbed conditions are examined on the basis of Greenland and Spitzbergen TV data. It is the present authors' new finding that characteristics of dayside auroras are quite different between the pre- and post-noon sectors. Namely, corona auroras are seen in the pre-noon sector and band auroras are seen in the post-noon sector. During the quiet period, corona auroras are observed at Magnetic Latitudes (MLAT) higher than 75 degrees in the pre-noon sector. In the post-noon sector, no remarkable auroras are seen around 75 degrees MLAT. On the other hand, during the disturbed period, corona auroras are observed at latitudes lower than 80 degrees MLAT in the pre-noon sector. Periodic bright band auroras appear in the post-noon sector. The comparison between these auroras and particle precipitation is also examined and the source region of dayside auroras is discussed.

静穏期と擾乱期の条件での昼側のオーロラの一般的な特徴を、グリーンランドとスピッツベルゲンでのテレビデータを基に調べた。昼側のオーロラの特性は、午前側と午後側で全く異なることが新たにわかった。すなわち、コロナオーロラは午前側に見え、バンドオーロラは午後側に見える。静穏期の間、コロナオーロラは地磁気緯度(MLAT)が75度以上の地域で午前側に観測された。午後側には、MLAT75度周辺では顕著なオーロラは見られなかった。一方、擾乱期の間、コロナオーロラはMLAT80度以下で午前側に観測された。周期的な明るいバンドオーロラは午後側に現れた。これらのオーロラと粒子降下との比較も試み、昼側のオーロラ源となる粒子降下領域についても論じた。